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python import class from different folder

my project has folders that are structured like this:
main
-folder 1
-file1.py
-folder 2
-file2.py
both file1 and file2 having classes.
when I try from main.folder1.file1 import class1 it fails, saying "No module named main". What am I doing wrong and how should I import it?

you have to first create the module by including __init__.py
in the root directory which is same in the hierarchy of main folder and also create an __init__.py in other sub folders to make them accessible as modules.
Here is an example structure from the official documentation.Note how at each level there is __init__.py you have to include similarly.
package/
__init__.py
subpackage1/
__init__.py
moduleX.py
moduleY.py
subpackage2/
__init__.py
moduleZ.py
moduleA.py
your structure can be like below:
main/
__init__.py
folder1/
__init__.py
file1.py
folder2/
__init__.py
file2.py
Then you can append the path to the module at the top level like below.
You can have it in the __init__.py in the root directory.
sys.path.append(path.dirname(path.dirname(path.abspath(file))))
Then try accessing like from folder1.file1 import class1.
This should resolve your problem.
To further understand your problem read about modules and how to include relative imports by referring documentation.

In python you have to declare each folder as a module by adding a file named __init__.py in each directory including the root. This file can be empty.

you can do this if there are one level above.
import sys
sys.path.insert(0,'../folder1')
sys.path.insert(0,'../folder2')
import function1
import function2
....
Once you run the first 3 lines, you are adding those folders to the working directory. You can then import the functions within those files as if they are in the file already.
If the folders are in the same level, do this,
import sys
sys.path.insert(0,'folder1')
sys.path.insert(0,'folder2')
import function1
import function2
....

How can we import python file form one directory to another directory?

I have a framework structure like
Stopper
/module1
file1.py
file2.py
__init__.py
/module2
file3.py
file4.py
__init__.py
runner.py
files.py
__init__.py
I want to import class or functions from file3.py to file2.py, as they are different directory.
Please let me know how to handle this scenario.
Thanks in advance.

Python3 import modules from folder to another folder

my structure dictionary is
mainFolder
folder1
__init__.py
file1.py
file2.py
folder2
__init__.py
file3.py
file4.py
setup.py
__init__.py
i need import file4.py from folder2 to folder1/file1.py
file1.py:
from ..folder2.file4 import MyClass
and i gets:
SystemError: Parent module '' not loaded, cannot perform relative
import
how to fix that ?

This is because you must to explicitly name the parent package.
So in your case you need either from mainFolder.folder2.file4 import Myclass, either from folder2.file4 import Myclass

Importing module with custom lookup

I have some problems with my project structure.
Because of historical reasons project looks like this:
Source/
__init__.py
module1/
__init__.py
script1.py
module2/
__init__.py
script2.py
and in production it deploys like this
server/
__init__.py
module1/
__init__.py
script1.py
module2/
__init__.py
script2.py
The problem is that script2.py has such imports:
from server.module1.script1 import something
Is it possible to say python to search server.*** not in server/*** but in Source/***?
Right now I made this with symlinks, but it looks ugly

You can always add keys to the sys.modules dictionary; these act as aliases for the module:
import sys
try:
import server
except ImportError:
import Source
sys.modules['server'] = Source
Once server is an entry in sys.modules, any sub-modules and packages will be found as well as the server entry will be used as a starting point for further imports.

python import within directory

I have a python project, I divided it into two parts, a library part and a
binary part.
For organization reasons, I wanted to have a hierarchy like this:
project/
lib/
__init__.py
module1.py
module2.py
bin/
binary1.py # contains: import module1
binary2.py # contains: import module2
doc/
...
The problem is, of course, the simple import in binary{1,2}.py doesn't work, at
least in the coding phase (before installation).
Any suggestions? How do you test your code when you're coding?

I use absolute imports everywhere.
project/
__init__.py
lib/
__init__.py
module1.py
module2.py
bin/
__init__.py
binary1.py # contains: import module1
binary2.py # contains: import module2
doc/
...
Setting PYTHONPATH to the directory above project, you can import module1 from binary1.py like this:
from project.lib import module1
The __init__.py files can make importing simpler, let's say in each file you have a class. Usually you would have to import the class like this (inclduding filename):
from project.lib.module1 import Module1
But if you edit lib/__init__.py to contain this line:
from project.lib.module1 import Module1
You can use the namespace of lib to import Module1 directly from lib:
from project.lib import Module1